Sextant and other angle measuring instruments



Jan. 12, 1954 SEIXTANT AND Filed 001;. 4, 1949 P. F. EVERITT ET AL OTHER ANGLE MEASURING INSTRUMENTS 4 Sheets-Sheet 1 /NVEN 7025 Pum Famous EVERITT JOHN KEEBLE 1954 P. F. EVERITT ET AL SEXTANT AND OTHER ANGLE MEASURING INSTRUMENTS 4 Sheets-Sheet 3 Filed Oct. 4, 1949 /NVENTOE$ PHlLlP FEANGS EVERITT Jo H N KEEBLE {I g g f ATTORNEYS Jan. 12, 1954 P. F. EVERITT ET AL SEXTANT AND OTHER ANGLE MEASURING INSTRUMENTS Filed Oct. 4, 1949 4 Sheets-Sheet 4 1 venior PHIL/9" FRANCIS um/Try JoH/v KEEBLE A tiorneys Patented Jan. 12, 1954 2,665,484 SEXTAN'I AND OTHER MEASURING I INSTRUMENTS Philip Francis Everitt Seven Kings, and John Keeble, Ilford, England, assignors, by mesne assignments, 7 to Kelvin & Hughes Limited,

Glasgow, Scotland, a British company Application October 4, 1949, Serial No. 119,492

Claimspriority,application Great Britain October 5, 1948 'lGlaims. 1

This invention relates to sextant's and other angle measuring instrumentssuch as theodolites, crystal goniometers and spectrometers, and especially but not solel'y to periscopic sextants for use in pressurised-aircraft.

According to the-inventionthe instrument'casing contains electric switches, gear'ch'ange devices, and/or other parts which are controlled from outside the casing by means of a control lever that is connected to a rocking shaft that passes through the casing, the lever being movable by the operator in one direction and spring returned so that the shaft rocks to and fro through a small angle; means are provided for utilizing a succession of such operativemovements of the shaft to eifect a series of operations within the casing including a movement WhlCh effects driving of a driven part by 'a electric motor and a movement which efiects stopping of said driven part when required, means for automatically stopping said driven part between said starting and stopping movements of the control lever if the driven part'reaches the end of a predetermined extent of tralvehwhereafter thestopping movement of the lever can nevertheless be effected without restarting the driven part, and the succession of movements ean then'be repeated.

A constructional form of the invention "will now be described by way of example with reference to the accompanying diagrammatic drawings wherein:

Figure 1 is a vertical sectional View of a penscopic sextant made in accordance with the invention;

Figure 2 is a sectional'view of the line 2-2 on Figure 1, omitting parts of thecasing;

Figure 3 is a view of part of the gear shift clutch lever 69 andparts lying to the right thereof in Figure 2 in the direction of the arrow A on Figure 2;

Figure 4 is a developed or exploded view of the reduction gearing, parts of which are shown in Figures 2 and 3;

Figure 5 is a sectional view on the line 5-5 on Figure 2;

Figure 6 is a sectional view on the line 6-6 on Figure 2; i

Figure '7 is a view showing the relative positions of certain cams; and

Figure 8 is an electrical diagram of the sextant.

The sextant comprisinga box-like casing 10, having a telescopic eyepiece II, a periscopic tube 12, a sighting prism to vary the angle of sight in accordance with the altitude of a celestial body I3, an arm 14 for adjusting the prism, a screw l5 for driving a nut 9 which in turn actuates the arm [4, a motor I 6, reversible'by manually operable switch means, not shown, for driving the screw, integrating means by means of which an average'value of the sight angle over a continuous period of adjustment may be obtained including balls l1 driven along a cylinder 18 by a rack l9 and pinion 22, integrating drums 26 which are reset to their initial indication after said continuous period as part of the mechanical average computing procedure, and degree and minute indicating drums 24, 25. The integrating mechanism is more fully described in copending United States Patent No. 2,652,976.

The pinion 22 is driven in one direction'at one speed during measurement of altitude, and is driven in the opposite direction at a greater speed for returning the parts to their initial positions. For this purpose the gearing shown more particularly in Figure 4 is provided in which a D. C. electrically governed permanent magnetic field constant-speed motor 28 (Figure 3) drives a spindle carrying a worm 29 driving a worm-wheel 30 which in turn rotates a wormiil in mesh with worm-wheel 32. The latter rotates a gear-wheel 33 in mesh with a sliding gear-wheel 34 which carries clutch teeth 35 on one side and clutch teeth 36 on'the other side. Teeth 35 can engage teeth 37 on the side of a gear-wheel 3a which meshes with atoothed wheel 39 on a spindle 40 which carries the pinion 22. The wheel 39 drives a dial it which indicates half the time of total measurement. The spindle also carries a'wheel 43 that gears with a pinion 46 on a spindle which carries the pinion 53.

The clutch teeth 36can-en'gage'clutch teeth 50, (Figure 2) on a rotary block 5| that carries a pinion 52 in mesh with'the gearwheel 53 (although in the exploded view of Figure 4 shown spaced therefrom) which drives the spindle 45 and pinion 22.

In order to control the clutch and various other parts of the sextant, there is provided a finger lever 8 outside the casing it] carried by a rocking shaft 9 that passes freely through an opening in the casing, the opening being covered by a rubber ring 54. Inside the casing the-shaft 9 carries an arm 56 that is normally held against a stop 51 by a'spring 58. The arm carries a pivoted pawl 60 that engages a ratchet wheel SI that has eight teeth, this ratchet wheel being mounted on a shaft 62. A pawl 53 prevents backward movements of the ratchet wheel and shaft 62. By these means, successive movements of the finger lever 8 rotate the shaft 62 one eighth of a revolution.

The shaft 62 carries a cam block 61 having a cam groove 68 in which a pin carried by a clutch or striking lever 59 is engaged, this clutch lever having a pin engaged in a groove 16 in a block 1I integral with the pinion 34 and clutch teeth 35, 36. The clutch lever is made in two parts pivoted together and held normally centralized by springs 12 which give if the clutch teeth clash when engaging.

The cam 68 is shaped so as to efiect the following movements of the lever 69 for each eight consecutive conditions of the lever 8, viz. forward drive position; no change, reverse drive position; no change, forward drive position; no change, reverse drive position; no change.

The shaft 62 also carries four cams 15, 16, 11, and 18 of insulating material having the shapes and relative dispositions shown in Figure 7 in the second operative positions (e. g. cam 15 is lion) The cam 15 operates a pair of spring blades 86 adapted to separate in order to provide a break in an electric current, controlling the motor 28 and provides the following eight consecutive conditions, viz: ofi, on, off, on, off, on, ofi, on.

Cam 16 operates a pair of blades 8| to give the conditions on ofi, on, off, on, off, on. ofi. this being the dial lighting switch.

Cam 11 controls two pairs of blades 62, 33 (which both open simultaneously and close simultaneously), for operating the integrator motor 28 and lighting of the optical parts of the sextant, giving the conditions on, on, off, off, on, on, off, off. Two of these blades (one of each pair) are connected together as shown by the double arrow in Figure 8.

Cam 18 controls a pair of blades 64 for reversing drive from the motor 28 and has the conditions off ofi, on, on, ofi, off, on, on.

v The above mentioned conditions are quoted with the same starting point, i. e., all the first mentioned conditions occur simultaneously.

In order to limit the stroke of the rack I9 in both directions two further cams 88, 89, are provided, these being mounted on the shaft 46 and controlling two pairs of switch blades 96, 9 I. Blades 9| switch off the motor and the bubble light at the end of the measuring run. Also a cam 93 on the shaft 46 controls the dial lighting through switch arms 94. Blades 96 stop the motor 28 and switch the dial light ofi when the various parts have been returned to the zero position but remain closed throughout the remainder of the measuring run.

Figure 8 shows an electric circuit diagram in which the altitude motor I6 which drives the screw I5 has one terminal connected to a lead I26 and the other connected to a lead I2I. The lead I2I is connected to one contact of a limit switch I64 operated by the nut 9 reaching one end of worm I5; the other contact is connected by a lead I22 to a switch contact I24 and through a resistance I25 to a switch contact I26. A pair of switch contacts I21, I28 are connected by a common lead I29 through a resistance I36 to a positive line I3I. A pair of contacts I33, I34 are connected to the limit switch I63 operated by the nut 9 reaching the other end of worm I5, the connection of the contact I33 including a resistance I31.

A pair of switch contacts I38, I39 are connected across the motor I6 and a pair of adjacent con- 4 tacts I46, I4I are connected by a common lead I42 to a negative line I43.

A hand operable lever I45 is connected to a hand operable lever I46 so that these levers move in unison. When they are moved in one direction (up in the figure) contacts I26, I21 connect and also I38, I46 to drive the motor I6 in one direction and further movement in the same direction connects I24, I26, I21, thereby cutting the resistance I25 out of the motor circuit to give faster drive. Movement of I45, I46 in the down direction drives the motor with two selectable speeds in the opposite direction.

The sextant includes the following illuminating devices:

1. Bubble ring light I61. This is a known type of sighting illumination which produces a ring of light reflected from the bubble.

2. Bubble daylight light I69. This form of illumination is used for sighting of the sun and produces a black disc in an illuminated field. The bubble is illuminated. In observations the sun is made to coincide with the centre of the bubble and the size of the bubble is adjusted so that its apparent diameter is larger than that of the sun. A black ring is then visible round the sun and this black ring is on the edge of the black disc produced by the bubble daylight light.

3. Bubble spot light I68. This type of lighting is used only for night sighting and is also known as red-spot lighting. The background is dark and the presence of the bubble is shown only by the presence of two red spots in a horizontal line. The star is placed between these for coincidence. The two spots are obtained by forming two images of a single lamp by means of two mirrors. The direct beam does not reach the collimating lens but since the bubble acts as a negative lens, light is refracted by the bubble into the lens and a minute image of the lamp is seen in the bubble.

4. Azimuth ring light I61. This consists of a small lamp illuminating the azimuth scale above it through a hole in the casing I6.

5. Dial lights I6I, I62. This consists of a lamp which illuminates the altitude scales.

A bubble ring light I61, bubble spot-light I68, and bubble daylight light I69 are selectively coupled by switch II6 through an adjustable resistance I66 (for dimming) and a resistance I56 to the positive line I3I. These lights are connected by a common lead I5I to one of a pair of contacts 83 the other of which is connected by lead I52 to one of the contacts 84, by a lead I53 to one of the contacts 9 I, and by a lead I54 to one terminal of the integrator motor 28. The other terminal of thev motor 28 is connected to one of the contacts 86 the other of which is connected to the line I3I. One of the contacts 82' is connected by lead I56 to the other contact 84 and by a lead I51 to the other contact 9I. The other contact 82 is connected to the negative line I43 by lead I59 and by lead I66 to one of the contacts SI. The other contact 8| is connected by lead I62 to one of the contacts 94 and by lead I63 to dial lights I6I, I62 which are in series and are connected through a resistance I65 to the peel tive line I3I. An azimuth ring light I61 is connected across the positive and negative lines by hand switch I65.

The other contact 94 is connected by line I19 to the negative line and to one of the contacts 96 the other of which is connected to one of the contacts 84.

Four successive movements of the control lever 8 are arranged to take the ratchet shaft through 180 whereupon the instrument is in normal position ready for a further succession of four movements. The four movements operate as follows:

1. The illuminating circuits are completed for illuminating the bubble and other parts of the instrument. The switch 90 being open and switch 9| being in the closed condition, the cam 75 leaves switch 80 off. The motor 28 is therefore not operated. Cam 16 connects blades 8| to illuminate dial lights Il, I02. Cam H closes switches 82, 83 as a cocking action. Cam 61, 68 is positioned for forward drive of the rack.

2. Cam 15 closes switch 80 to complete the circuit of motor 28 through switches 8|, 82. Cam 16 switches off dial lighting during the forward run. The bubble lighting remains on. The motor 28 is automatically switched off by cam 88 opening switch 9| at the end position of the movement of the ball cage and the bubble illumination switched off, unless these actions are otherwise eifected by a third movement of the control lever before this position is reached. The dial light also comes on again by cam 93 closing switch 94 at the end position of movement, again provided the third lever movement does not occur first and effect this result.

3. This lever movement stops the motor 28 by cam 15 opening switch 80 and cam 11 opening switches 82, 83 unless already stopped by cam 89 opening switch 9| in which case this lever movement only moves the switch 80 to its 01? position ready for its next movement. The dial light comes on or remains on, other lights go off or remain oil. Cam 88 closes switch 90. Cam 18 also closes switch 84 in readiness for reversing drive of the motor 28.

4. Cam l5 closes switch 80 and completes circuit of the motor 28 through switches 84, 90. The striking lever 89 changes gear and the drive from the integrator motor is driven in reverse to return the ball cage or rack H! at a higher speed to starting position and is there again automatically switched off by means of cam 88 opening the switch 90. The dial light is extinguished by cam 16 opening switch 8| so that all lights are now off.

We claim:

1. An angle measuring instrument having a casing, optical sighting means in the casing, sight angle varying means in the casing, a first motor in the casing for actuating the angle varying means in the forward and reverse directions, dial indicating elements, integrating means, a second motor for driving the integrating means, said integrating means comprising a variable input means connected to said angle varying means and an output connected to feed a resultant movement to at least one of said elements, first limit switch means operated by said angle varying means for switching off the first motor at opposite limits of movement of the angle varying means, second limit switch means for switch ing off the second motor at opposite limits of drive of the integrating means, cams driven by the second motor for operating said second limit switch means, lighting means in the casing, a plurality of control switches in the casing for controlling the lighting means and the second motor, a reversing gear through which the second motor drives the integrating means, a reversing element for reversing said gear, a rotary cam in the casing for actuating said reversing element, a rocking shaft carrying said cam and extending to a position outside the casing, a control lever outside the casing and connected to said rocking shaft, the lever being manually movable in one direction, spring means for effecting return movement of the lever in the opposite direction, a plurality of cams on said shaft positioned for operating said control switches, whereby a succession of movements of the shaft effects a required sequence of operations of the said switches including actuating the switches for switching the second motor off and on and switching the lighting means off and on and mov ing the reversing gear from forward drive to reverse drive and from reverse drive to forward drive.

2. An instrument as claimed in claim 1 wherein the reversing gear includes quicker reverse drive means than the forward drive.

3. An instrument as claimed in claim 1 Wherein the lighting means include first lighting means for dial illuminating and second lighting means for lighting the sighting means, one of said control switches being in the circuit of the first lighting means, another of said control switches being in the circuit of the second lighting means,

cam driven by the second motor operating said dial lighting switc 4. In an angle measuring instrument having result indicating means, electric lighting means and an electric motor for operating the indicating means, the provision of a plurality of control switches including at least one in the motor circuit and at least one in the lighting means circuit, a reversing gear through which the moto drive it step by step, and a plurality of cams on said shaft positioned for operating said control switches, whereby a succession of movements of the shaft effects a required sequence of operations of said switches and actuation of the reversmg gear.

PHILIP FRANCIS EVERI'IT.

JOHN KEEBLE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,386,032 Simmon Aug. 2, 19 1 1,606,785 Hodgkins Nov. 16, 1926 1,766,656 Kuntze et al June 24, 1930 2,145,938 Mansfield et a1. Feb. 7, 1939 2,276,674 Schroeder Mar. 17, 1942 2,304,770 Nichols Dec. 8, 1942 2,399,530 York et a1. Apr. 30, 1946 2,456,392 Doyle Dec. 14, 1948 2,516,187 Deimel et a1 July 25, 1950 FOREIGN PATENTS Number Country Date 525,801 Great Britain Sept. 4, 1940 581,722 Great Britain Oct. 23, 1946 946,903 France Dec. 27, 1948 

